Re: swap utilisation is ver high but not memory utilisation

Swap utilization is high because it is all reserved, not because there's any data on the devices. (You have 175800Mb of swap, and 168549Mb of it is reserved). [Note that none of the devices show anything but 0Mb in the Used column of glance/"w", and this matches the observation of no pageouts].

Processes must reserve swap when non-file backed virtual objects are created (barring use of lazy swap options via chatr, mmap flags, etc.). This is to ensure the system has swap blocks available if and when a pageout must occur. So your workload has a virtual requirement which is almost at your available swap space taking into account both device swap and memory swap.

If things remain this way -- you do have about 7Gb of virtual address space remaining, so this may simply be a well-tuned load for the box. If it pushes to 100%, however, you would start to see failures from malloc, fork, mmap, etc. with ENOMEM so you'd want to either add more swap before that point or throttle down the workload.

The first part says that if you request virtual memory for shared memory, heap or private mmap, you need to reserve swap space. Shared mapped files don't need it.The second part says if you are tricky and use lazy swap, then it doesn't reserve it.

>are there lots of processes that have reserved virtual memory?

There may be few that reserve lots of memory, it's the sum of the requirements.

>Do we need to add swap space so that more and more processes could be started.

Yes, either that or more memory.

>Also if more and more processes are started is pages in be very high?